1. Field of the Invention
The present invention generally relates to radio communications systems and particularly relates to user apparatuses and paging channel reception methods.
2. Description of the Related Art
In a radio communications network, a location of user apparatuses is stored in a network in units of tracking areas. The tracking area, which corresponds to a location area (LA) or a routing area (RA) in 3G, includes one or more cells.
An access gateway apparatus which manages each of the user apparatuses has an identifier of the access gateway apparatus held in a home location register (HLR).
A user apparatus has two types of operating modes, i.e., an active mode and an idle mode.
A user apparatus in the idle mode or a user apparatus in a camping status selects a cell to camp on according to a propagation state, and receives a paging channel transmitted from the cell. The user apparatus checks for the paging channel received, checks for the presence of a signal indicating transmission incoming to the own apparatus and, upon determining that there is a signal indicating the transmission incoming to the own apparatus, accesses, in uplink, the cell it visits. Then, the user apparatus establishes a connection with the cell and changes to the active mode. At this time, the network is able to specify a cell visited by the user apparatus.
When the user apparatus is in the idle mode, there is no connection established with the user apparatus, so the network is not able to specify the cell visited by the user apparatus. Thus, the network transmits a paging channel at all cells belonging to the tracking area.
In each of the tracking areas, an identifier of the tracking area is reported from the corresponding cells. The user apparatus in the idle mode receives the reported identifier of the tracking area, so that it may determine the tracking area the own apparatus visits.
For example, when the identifier of the tracking area that is reported at a neighboring cell to which the user apparatus moves is different from a previously-reported identifier of the tracking area, the user apparatus accesses in uplink and requests for updating location registration. Such an updating of the location registration is called a tracking area update (TAU). More specifically, the user apparatus stores and holds an identifier of the tracking area to which location registration is made. The user apparatus performs a re-selection of a cell in conjunction with the move. Such a re-selection of the cell is called a cell re-selection. Each time a mobile station performs the cell re-selection, it receives broadcast information from the cell, and checks for an identifier of the tracking area included in the broadcast information. When an identifier of a new tracking area that is received is different from an identifier of a tracking area that is stored and held, it is determined that a tracking area previously visited has been exited, so that a tracking area update is performed. When the tracking area update is performed, the network reports, to the user apparatus, an identifier of a tracking area which has the user apparatus registered, and the user stores and holds the reported tracking area identifier. Then, the network may report an identifier for multiple tracking areas. In this case, the user apparatus performs the location registration of the multiple tracking areas at the same time. This is called a multi-TA registration. The user apparatus compares the tracking area identifier stored and held with the identifier of the tracking area reported at the cell re-selected in the cell re-selection so as to determine whether the tracking area update is needed.
On the other hand, if the identifier of the new tracking area that is received is the same as the stored and held tracking area identifier, the user apparatus determines that it has not exited the tracking area it has previously visited. In this case, the user apparatus does not perform the tracking area update.
In conjunction with the move, the user apparatus performs the cell re-selection, but does not perform the tracking area update as long as the tracking area visited is the same.
Moreover, a user apparatus in an active mode, i.e., a user apparatus in communication, does not have to perform the tracking area update.